Retatrutide vs. Tirzepatide
Evidence checked November 6, 2026 · United States
Retatrutide and tirzepatide act on different combinations of hormone receptors and have different approval statuses. Tirzepatide is FDA-approved under the brand names Zepbound and Mounjaro for specific uses. Retatrutide is investigational. Both have produced substantial average weight loss in separate placebo-controlled trials. The direct comparison, TRIUMPH-5, has yet to report public results as of November 6, 2026. ClinicalTrials.gov registration · FDA guidance
On this page · Key differences · Weight-loss trial results · Head-to-head evidence · Side effects and safety · U.S. approval and availability · Frequently asked questions · Research publications and official sources
Retatrutide vs. tirzepatide at a glance
| Feature | Retatrutide | Tirzepatide |
|---|---|---|
| Receptors targeted | GIP, GLP-1 and glucagon | GIP and GLP-1 |
| U.S. status | Investigational | FDA-approved for specific uses |
| Phase 3 obesity evidence | TRIUMPH-1 compared retatrutide with placebo at 80 weeks | SURMOUNT-1 compared tirzepatide with placebo at 72 weeks |
| Direct comparison | TRIUMPH-5 is the registered head-to-head trial | Tirzepatide is the active comparator in TRIUMPH-5 |
How do the drugs work?
An agonist activates a receptor. Both drugs activate receptors for glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). Retatrutide also activates the glucagon receptor. That third target is a pharmacologic difference. Clinical trials are needed to determine how it affects outcomes and tolerability. Retatrutide discovery and proof-of-concept study · Tirzepatide prescribing information
Retatrutide vs. tirzepatide weight-loss trial results
The two pivotal studies below randomized adults without diabetes to an active drug or placebo. The figures show estimated average reductions from starting body weight in each study’s analysis designed to account for participants regardless of whether they continued treatment.
| Phase 3 trial | Time point | Mean weight reduction |
|---|---|---|
| TRIUMPH-1 · Retatrutide (2,339 randomized) | 80 weeks | 17.6%, 23.7% and 25.0% across the three study dose groups, versus 3.9% with placebo |
| SURMOUNT-1 · Tirzepatide (2,539 randomized) | 72 weeks | 15.0%, 19.5% and 20.9% across the three study dose groups, versus 3.1% with placebo |
Retatrutide’s earlier phase 2 study followed participants for 48 weeks. TRIUMPH-2 separately studied adults with obesity or overweight and type 2 diabetes. Tirzepatide’s SURMOUNT-2 also studied adults with obesity or overweight and type 2 diabetes. For that population, use the diabetes-specific publications to understand the results and their limitations. Retatrutide phase 2 trial · TRIUMPH-2 · SURMOUNT-2
Why the studies cannot tell us which drug works better
Subtracting the two trial averages would mix different follow-up periods, participants, and study protocols. Each study answers how its own treatment groups compared with its own placebo group. TRIUMPH-5 assigns participants within the same trial to retatrutide or tirzepatide, making a direct comparison possible when its results are available. TRIUMPH-5 registry · Sponsor trial record
The similar trial names can be confusing. TRIUMPH-5 compares retatrutide with tirzepatide. SURMOUNT-5 is a published comparison of tirzepatide with semaglutide in adults with obesity. A separate sponsor report compared retatrutide with semaglutide in adults with type 2 diabetes. Those semaglutide comparisons answer different questions. SURMOUNT-5 publication · October 2026 sponsor topline report
Side effects, safety and longer-term evidence
Retatrutide. Gastrointestinal symptoms were the most common adverse events in TRIUMPH-1. The earlier phase 2 study also reported dose-related increases in heart rate that peaked at week 24 and later declined. Trial results help characterize adverse events in enrolled participants, while longer follow-up helps assess uncommon or delayed effects. TRIUMPH-1 safety findings · Phase 2 safety findings
Tirzepatide. Common Zepbound side effects include nausea, diarrhea, vomiting and constipation. Its U.S. label carries a boxed warning about thyroid C-cell tumors observed in rats, with uncertain relevance to humans. The label lists a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 as contraindications. Other warnings include pancreatitis, gallbladder disease and kidney injury from dehydration. Full Zepbound prescribing information
Weight maintenance. In SURMOUNT-4, participants who continued tirzepatide after a 36-week lead-in maintained more of their initial weight loss than participants switched to placebo. A separate three-year analysis followed participants with obesity and prediabetes. These studies provide information beyond the initial weight-loss period. SURMOUNT-4 maintenance trial · Three-year SURMOUNT-1 analysis
U.S. approval and availability
- Zepbound is approved for long-term weight reduction and maintenance in adults with obesity or with overweight and a weight-related condition. It is also approved for moderate to severe obstructive sleep apnea in adults with obesity. Zepbound label · SURMOUNT-OSA trial
- Mounjaro is approved to improve blood sugar control in adults and children aged 10 and older with type 2 diabetes, alongside diet and exercise. It is also approved to reduce the risk of major cardiovascular events in adults with type 2 diabetes who are at high risk for those events. Mounjaro label · SURPASS-CVOT trial
- Retatrutide remains investigational. The FDA states that retatrutide cannot be used in compounding under federal law. For clinical research, check the trial registry for current study details and eligibility. FDA guidance on unapproved products · ClinicalTrials.gov
Frequently asked questions
Is retatrutide stronger than tirzepatide?
The published placebo-controlled trials cannot establish which drug produces more weight loss under the same conditions. TRIUMPH-5 was designed to answer that question directly. Follow the head-to-head trial
Is retatrutide FDA-approved for weight loss?
No. Retatrutide remains investigational in the United States as of November 6, 2026. FDA guidance
Is tirzepatide the same in Zepbound and Mounjaro?
Both brands contain tirzepatide. They have distinct U.S. prescribing labels and approved uses. Zepbound label · Mounjaro label
Do the published percentages predict how much weight I would lose?
The percentages are group averages. Individual results vary, and a trial population may differ from a person seeking care. A clinician can explain which evidence applies to your health history and goals. Read the patient guide to online weight management
Research publications and official sources
The links below lead to original research papers, the trial registry, or official U.S. prescribing information. Several pivotal studies were funded by the manufacturer. The papers identify sponsors, methods and disclosures.
- Jastreboff and colleagues · TRIUMPH-1 — phase 3 obesity trial, NEJM (2026).
- Jastreboff and colleagues · Retatrutide phase 2 — early placebo-controlled obesity trial, NEJM (2023).
- Bellido and colleagues · TRIUMPH-2 — phase 3 obesity and type 2 diabetes trial, The Lancet (2026).
- TRANSCEND-T2D-1 — phase 3 retatrutide trial in type 2 diabetes, The Lancet (2026).
- LY3437943 discovery and clinical proof of concept — original receptor and early clinical research, Cell Metabolism (2022).
- Jastreboff and colleagues · SURMOUNT-1 — initial 72-week tirzepatide obesity trial, NEJM (2022).
- Garvey and colleagues · SURMOUNT-2 — weight management in adults with type 2 diabetes, The Lancet (2023).
- Aronne and colleagues · SURMOUNT-4 — randomized withdrawal and weight maintenance, JAMA (2024).
- Jastreboff and colleagues · Three-year SURMOUNT-1 analysis — outcomes in participants with obesity and prediabetes, NEJM (2025).
- Aronne and colleagues · SURMOUNT-5 — tirzepatide compared with semaglutide for obesity, NEJM (2025).
- Malhotra and colleagues · SURMOUNT-OSA — tirzepatide for obstructive sleep apnea and obesity, NEJM (2024).
- Nicholls and colleagues · SURPASS-CVOT — tirzepatide versus dulaglutide cardiovascular outcomes in type 2 diabetes, NEJM (2025).
- TRIUMPH-5 · NCT06662383 — registered retatrutide versus tirzepatide trial.
- FDA guidance on unapproved GLP-1 drugs · Zepbound label · Mounjaro label.
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This article summarizes published evidence for general education. A licensed clinician can help apply it to an individual treatment decision.